The present invention relates to an encoding system of a simulcast high definition television and a method thereof, and more particularly to an encoding system and a method for transmitting a high definition television (hereinafter referred to as HDTV) signal through a presently used VHF or UHF channel by using a HDTV bandwidth compression utilizing the three-dimensional sub-band coding, adaptive modulation, scrambling, double side band-quadrature modulation (DSB-QM), data-under technique, in a land simulcast HDTV for transmitting an image signal of high picture quality and an aural signal of high tone quality through an NTSC transmission channel by compressing bandwidth with a sub-band coding method.
In a HDTV, real studies for a simulcast system bandwidth-compressing an image signal of high picture quality and an aural signal of high tone quality by a sub-band coding technique and transmitting the bandwidth-compressed signal to a presently used NTSC transmission channel has done from the year 1983 at MIT (Massachusetts Institute of Technology). The system proposed by MIT is being watched in that there is no necessity for newly establishing and increasing an additional transmitting system or a relay equipment because of the VHF or UHF channel being used as a transmission channel even if it is not compatible with the presently used NTSC system television set. In the above simulcast system, since the image information having high picture quality should be transmitted to a taboo channel, i.e., a 6 MHz band of an unused channel between channels in order to exclude interference caused by the transmission between adjacent channels, the bandwidth compression technique is important. Moreover, in order to prevent from the adjacent inter-channel interference, a transmission signal level must be reduced. Thus, a method for digitally transmitting a direct current (hereinafter referred to as the DC) component of the transmission signal, or minimizing the level of a modulation signal by using the DSB-QM of a carrier suppression modulation technique is considered. Further, in order to reduce a channel noise or a ghost, scrambling is performed, with the result that the improved picture quality can be obtained by uniformly distributing the noise and ghost appearing as dense forms at a narrow region to the entire region of a screen. In addition, there is an adaptive modulation system for reducing the noise of a transmission channel. That is, in a transmitting side, an image signal of a low level is amplified up to the maximum allowable transmission level and an adaptive constant, i.e., an amplification coefficient is digitally transmitted to a receiving side. Thereafter, in the receiving side, the received image signal is divided by the adaptive constant. Accordingly, since the received image signal is restored to the original signal level and the channel noise is also divided, the channel noise is reduced as much as the divided adaptive constant.
FIG. 1 is a block diagram of an encoding system according to the above described MIT proposal system. An image signal of high picture quality from a high-rate production system 1 is digitally converted in an analog to digital (A/D) converter 2 and is applied to a quadrature mirror filter (QMF) bank 3. The QMF bank 3 transmits corresponding sub-blocks among forty-five sub-blocks to a multiplexer 4, in response to a motion detection mode of an input signal, as shown in FIGS. 2A to 2F. Moreover, aural data D.sub.A and transmission data D.sub.D are applied to the multiplexer 4. In this case, the transmission data D.sub.D represent data output from a facsimile, a telex, a telephone, etc. The multiplexer 4 time-divisionally multiplexes the sub-block from the QMF bank 3, the aural data D.sub.A and the transmission data D.sub.D under the control of a controller 6 so as to generate nine sub-blocks. The three sub-blocks of R.G.B (red, green and blue) as shown in FIG. 2A and the three base band sub-blocks of V1, H1 and T1 as shown in FIG. 2B are always transmitted, and the three sub-blocks shown in FIGS. 2C to 2F are additionally transmitted according to the motion detection mode. For example, if the input image signal is a still picture, the three sub-blocks of V2, VH and H2 shown in FIG. 2C are added to the sub-blocks of FIG. 2B, and if it is a semi-motion picture, the three sub-blocks of T2, VT and HT shown in FIG. 2D are adder thereto. Moreover, if it is a motion picture, the three sub-blocks of T2, T3 and T4 shown in FIG. 2E are added to the sub-blocks of FIG. 2B, and if the input image signal is a movie picture, etc., the three sub-blocks of VH, VT and HT shown in FIG. 2F are added thereto. In this case, the unit of a vertical axis f.sub.V is the number of lines per picture height (hereinafter referred to as the LPH), the unit of a horizontal axis f.sub.H is the number of samples per picture width (hereinafter referred to as the SPW) and the unit of a time axis f.sub.T is the number of frames per second (hereinafter referred to as the FPS).
Next, in a storage circuit 5 of FIG. 1, the time-division multiplexed data is scrambled by the control of the controller 6, and in order to transmit the scrambled data to a transmission channel of 6 MHz, the DSB-QM is performed with formats shown in FIGS. 3A and 3B in a modulating unit 100. In this case, the scrambled data from the storage circuit 5 has in-phase channel data I as shown in FIG. 3A and quadrature phase channel data Q shown in FIG. 3B. In FIGS. 3A and 3B, a L1 is two lines for transmitting a vertical synchronizing signal, a line L2 is for transmitting the image signal and a L3 having 105 lines is for transmitting the aural data D.sub.A and the transmission data D.sub.D. In the modulating unit 100, the in-phase channel data I is applied to a first D/A (Digital to Analog) converter 50 and the quadrature channel data Q is applied to a second D/A converter 52, so as to produce analog signals.
In a mixer 62, the low-pass filtered in-phase channel signal through a first low pass filter (LPF) 54 at 3 MHz is mixed with a signal from a 90.degree. phase shifter 60, where a carrier through C.sub.in is 90.degree. phase shifted, and is modulated. The low-pass filtered quadrature channel signal through a second LPF 56 at 3 MHz is mixed with the carrier through C.sub.in of a mixer 58 and is modulated. The modulated in-phase and quadrature channel signals are added in an adder 64 to produce a radio frequency signal S.sub.out. In this case, in the storage circuit 5, Data D.sub.out of 8.4 Mbyte/sec or 12 Mbyte/sec for optical transmission may be produced, and a signal S'.sub.out for satellite communication of frequency modulation (FM) may be generated through a third D/A converter 7 and a third LPF 8. The third LPF 8 low-pass filters at 6 MHz. Since the DSB-QM is a transmission system that a transmission signal is divided into two channels of an in-phase channel and a quadrature phase channel having a phase difference of 90.degree., it can raise the channel efficiency by two times. In this case, in order to reduce the adjacent inter-channel interference, algorithm for suppressing the radio frequency carrier and removing a DC component is used. Meanwhile, a base band image signal is divided into forty-five sub-blocks in the ratio 3:3:5 in respect to the horizontal axis (H): vertical axis (V): time axis (T), by the three-dimensional sub-band division method in the MIT proposal system. The division of the ratio 8:8:3 with respect to the horizontal axis (H): vertical axis (V): time axis (T) may be possible. Moreover, in the process of the DC component, a luminance low frequency component with respect to four base sub-blocks is processed in two bits, and R-Y and B-Y of a chrominance component are processed in 1 bit, respectively. The signal transmission is performed through a data-under-channel with a form totally superposing an analog signal and a digital signal, and for an adaptive modulation, an adaptive constant and adaptive modulated image information is processed with the data-under.
As described above, the MIT proposal system suggests basic idea for various techniques. However, the detailed technique and definite hardware is not established.